Treatment of frictional surfaces to facilitate wearing-in



PATENT OFFICE L'REATMENT OF FRICTIONAL SURFACES TO FACILITATE WEARING-IN Bruce B. Farrington, Berkeley, Robert L. Humphreys, El Segundo, and Ronald T. Macdonald, Berkeley, Calif., assignors, by mesne assignments, to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Original application August 7, 1939, Serial No. 288,834, now Patent No. 2,311,653, dated February 23, 1943. Divided and this application October 31, 1941, Serial No. 417,354

9 Claims.

This invention relates to the treatment of metallic frictional surfaces of machine elements and especially to a treatment which prevents scufling or seizing of moving mechanical elements in frictional contact during the breaking-in process.

Because of the increased power and increased speed of moving parts of recently designed automobiles, it has been found that formerly suitable lubricants are not capable of providing safe lubrication. This is especially true during the breaking-in process and in the case of cars provided with hypoid gears. Various lubricants have been developed in an effort to meet the extreme requirements necessary to insure absolutely safe lubrication under the high pressures and sliding friction encountered in modern machines.

The problem of lubricating hypoid gears has become particularly acute. Lubricants which have been provided for these gears can be classifled into two general types, namely, (1) corrosive extreme pressure lubricants containing, for instance, free sulfur or corrosive oil-soluble sulfur compounds, and (2) milder extreme pressure lubricants containing non-corrosive oil-soluble compounds of sulfur or other materials which eventually react with the metallic surface being lubricated to form a protective film which prevents scufllng or seizure. The significance .of the term "non-corrosive extreme pressure lubricant is in general well understood in the lubrication art. As an example 'of the line of division between corrosive and non-corrosive extreme pressure lubricants, such a lubricant of the sulfur-bearing type is regarded as corrosive if it darkens a polished copper strip immersed in the lubricant for onehalf hour at 300 F., and is regarded as noncorrosive if no discoloration occurs under these conditions.

In testing gears and gear lubricants, we have found two characteristics to be generally true: first, that lubricants containing free sulfur or other distinctly corrosive materials used in corrosive extreme pressure lubricants allow new gears to be safely broken in under heavy loads with little danger of scuffing. However, such lubricants are not desirable for continued use after the gears have been "run-in because of detrimental efiects on bearings and other parts and because of accelerated wear produced on the gears. Of course detrimental action on bearings occurs to some extent even during breaking-in. Nevertheless, corrosive lubricants are being used because they have been regarded as essential.

The second eflect which has been found to be true is that less corrosive extreme pressure Thus the corrosive extreme pressure lubricants are more desirable than the non-corrosive because of increased film strength, but are less desirable because of corrosive action on bearings and because they produce an accelerated wear rate after continued use.

This invention avoids the above difiiculties and provides a method of eliminating the necessity for highly corrosive extreme pressure lubricants, and in some cases the necessity of even mild or noncorrosive extreme pressure lubricants, during breaking-in of machine elements. The present invention also provides a method which facilitates running-in of closely fitting machine parts, such as piston rings and cylinder walls of internal combustion engines, where it is not feasible to use an extreme pressure lubricant.

Accordingly, an object of this. invention is to eliminate the necessity of highly corrosive extreme pressure lubricants.

It is also an object of the invention to provide a process of treating gears and other mechanical elements, subject to metal-to-metal contact, so that danger of scllffing or seizing is avoided during the breaking-in process, even though noncorrosive lubricants are used and the raw gears or other elements are immediately run under conditions which would normally produce scuffing, such as heavy loads and high speeds.

Another object of the invention is to form by chemical action an integral thin tenacious coating on the teeth of gears prior to running-in" and then to run-in such gears with a mild or non-corrosive extreme pressure lubricant.

A still further object of the invention is to provide an integral thin tenacious coating on the pistons, piston rings and/or cylinder walls of an internal combustion engine, by chemical reaction with the metal surfaces, whereby breaking-in of these parts is facilitated and scoring is avoided.

Metal surfaces may be treated according to our invention with the reagents of the type hereinafter disclosed in a great number of ways to form reaction products with the metal surfaces and to give the desired action. It is obvious that in all cases strength of treating agent, temperature,

the time of treatment, should be adjusted so asv to yield an integral, non-flaky, thin, tenacious film on the metal surfaces. The necessary conditions and adjustments are within the knowledge and are apparent to those skilled in the metal I ah 3 treating art. These conditions can be determined by simpletests.

It is also. apparent that in the case of treatment of gears, either the entire gear or only the teeth thereof may be treated.

Three general types of treatment may be utilized:

(1) Treatment with gases.-As an example of this type, ferrous metal may be treated with hydrochloric acid vapors containing moisture. 1o

(2) Treatment with liquids.-In this type of process, gears may be dipped, sprayed or painted with aqueous solutions of suitable water-soluble acids. Instead of the acids themselves, materials which will hydrolyze or decompose to give the free acid may be used. The treated metal is subsequently dried and when necessary, heated to effect chemical combination of the treating agent and the metal base. Likewise, the metal may be treated with colloidal suspensions of the acid or other suitable active ingredient. Where the treating agent is a liquid or can be melted at suitable temperatures the material itself in liquid phase may be utilized.

Treatment of ferrous metals with liquids may of time are required, depending on the rate of reaction in each. case. Temperatures of between 160 and 200 F. have been found to be most suitable.

To compare the utility of the films produced by the present invention, a testing machine of the type described in the S. A. E. Journal of December 1933, at page 402, was used. The steel cups used in this machine were washed and thoroughly cleaned in organic solvents. A bath of approximately 200 cc. of the acid solution (aqueous solutions were used unless otherwise indicated) was heated to a temperature of from 160 F. to about 200 F. and the steel cups to be treated were introduced for varying periods of time. In order to compensate for different reaction rates, the amount of reaction was usuaily estimated by the coloring produced on the metal and was permitted to proceed to about the same degree in each case. Where reaction rates were slow and of comparable rate, or where no coloring was produced, treatment was carried out for a given constant length of time.

A non-corrosive extreme pressure mineral oil lubricant containing a lead soap and sulfurized fatty oil was used for lubrication during the above tests. This lubricant alone carried a load of approximately 85 pounds on the untreated metal cups in the testing machine. The following table of experimental results shows the greatly increased load carrying capacity of the same lubricant after pretreatment of the frictional surfaces according to'this invention.

Load carrying capacities 0 Treatment oncen- Test tration, Agent weight Structural formula Average Dum: (ililgsat per cent temp., tion,

F. mins.

Untreated surface 85 Hydroxy acids:

0 O OH 10 190 1 540+ Citric acid. CO0HCH=-C-CHr-COOH OH OH Tartaric acid 10 C O OHOHCHC O OH 185 30 572 (|)H Malic acid 10 C O OH-CHC Hz@ 0 OH 170 10 452 ()H Lactic acid l0 CHz-GH-C O OH 170 441 OH ([)H ?H (|)H ?H Gluconica'cid 10 (SHpCH-CH-CIL-CH-C 0 OH 185 15 418 Unsubstltuted acids:

Suocinicacid 10 C0 OH-CHzCH3-COOH 185 30 219 Oxalic acid 10 C 0 011-0 0 OH 186' 30 223 Acetic acid l0 CHz-C O OH 185 30 215 Unsaturated acid: Maleic 10 C O 0HCH=CHC O O H 165 10 564 acid.

1 Cups were not cut when machine automactiwally shut down at full load. Variations in shutdown load are due to difiiculty in resetting controls on machine.

(3) Treatment with solids.Another mode of operation is to dust the metal with a solid treating agent and produce chemical reaction by heating or by addition of small amounts of water to enable the acid to attack the metal.

The preferred method of treatment consists in exposing ferrous metal surfaces to the action of aqueous solutions of various organic acids of 7 the type hereinafter described. Varying periods than one by comparing the results with tartaric acid (572 lbs.) and of malic acid (452 lbs).

The unsaturated carbons adjacent to the carboxyl groups in maleic acid (564 lbs.) show a highly beneficial effect when compared with results obtained from succinic acid (219 lbs).

It is evident from the above presented facts that when steel surfaces are treated with watersoluble organic acids disclosed herein, increased load carrying capacities are obtained. Monoand poly-basic acids, both saturated and unsaturated, unsubstituted and substituted with hydroxy substituents comprise effective treating agents.

It is also apparent from the above disclosure that there are many acids within the scope of our invention which have sufficient activity to attack the metal surface to be treated and to form thereon the required integral tenacious adherent film.

When treating case-hardened metals, the treatment should be controlled so that only a portion of the hardened encasing metal is attacked by our reagents. The remaining portion of the hardened metal is then retained and there is no substantial alteration in the hardness of the underlying metal surface of the treated article.

While the invention provides a means for running-in new gears with non-corrosive extreme pressure lubricants, it is also applicable to use with extreme pressure lubricants that are mildly corrosive. For conditions of operation in which very active or corrosive extreme pressure lubricants have heretofore been required to prevent scuffing during running-in, less corrosive extreme pressure lubricants may be rendered usable and satisfactory by pretreating the frictional surface as herein described. For example, corrosive extreme pressure lubricants containing up to 1% free sulfur have heretofore been found inadequate to prevent scuffing of gears under certain breaking-in conditions. This same lubricant prevents such scuffing under the same conditions when used with gears pretreated according to this invention.

While in many cases the film formed by our pretreatment is eventually removed by wear, tests have shown that the scoring of new frictional surfaces generally occurs in the early stages of use, particularly when heavily loaded. Our pretreatments provide a protecting film which is resistant to extreme pressures, and which prevents scoring or seizing during this initial critical period. Consequently our invention also has utility for breaking-in machine elements where the object is merely to insure proper wearing-in of the l parts and it is not necessary or desirable to use extreme pressure lubricants. Accordingly the pretreatment described in this invention is appli-- cable to piston rings and/or cylinder liners of internal combustion engines and. when applied thereto facilitates breaking-in of a new motor.

The phenomenon responsible for the surprising results obtained by combining our pretreatment with the use of non-corrosive extreme pressure lubricants may be a catalytic one. The preformed films themselves are worn off in use by friction. However, these preformed films seem to act as a catalyst and facilitate reforming of a new film by the non-corrosive extreme pressure lubricant as soon as parts of the old film are worn off. In the absence of these preformed films, the noncorrosive extreme pressure lubricants are less efficient in preventing scuffing and seizing during running-in of metal parts, presumably because initial formation of the film takes place more slowly. Irrespective of the above catalytic theory, which is not regarded as essential to the invention, we have discovered a physical effect resulting from a particular combination of process steps which greatly facilitates lubrication of hypoid gears and other mechanical elements where ferrous metal to ferrous metal frictional contact under high pressures is involved.

Our application Serial No. 93,920 filed August 1, 1936, was forfeited and was renewed as application Serial No. 288,834,; filed August 7, 1939, now Patent No. 2,311,653. The present application is a division of said last application Serial No. 288,834.

We claim:

1. In a process for breaking-in machine elements having ferrous metal frictional bearing surfaces which after assembly of the elements and said surfaces in closely fitting and lubricated operative relationship tend to become scuffed and scored during the initial stage of operation, the improvement which comprises, prior to the assembly and operation of said elements pretreating one of said ferrous surfaces with a watersoluble carboxylic acid having a hydroxy substituent under suitable conditions to cause chemical interaction therebetween, and for a period of time sufiicient to preform on said surface an integral thin tenacious film adapted to facilitate and prevent scuffing and scoring during the breaking-in operation.

2. In a process for breaking-in machine elements having ferrous metal frictional bearing surfaces which after assembly of the elements and said surfaces in closely fitting and lubricated operative relationship tend to become scufied and scored during the initial stage 0f operation, the improvement which comprises, prior to the assembly and operation of said elements pretreating one of said ferrous surfaces with a water-soluble polycarboxylic acid having a hydroxy substituent under suitable conditions to cause chemical interaction therebetween, and for a period of time sufficient to preform on said surface an integral thin tenacious film adapted to facilitate and prevent scuffing and scoring during the breaking-in operation.

3. In a process for breaking-in machine elements having ferrous metal frictional bearing surfaces which after assembly of the elements and said surfaces in closely fitting and lubricated operative relationship tend to become scuffed and scored during the intial stage of operation, the improvement which comprises, prior to the assembly and operation of said elements pretreating one of said ferrous surfaces with a watersoluble polycarboxylic acid under suitable conditions to cause chemical interaction therebetween, and for a period of time sufficient to preform on said surface an integral thin tenacious film adapted to facilitate and prevent scufllng and scoring during the breaking-in operation.

4. In a process for breaking-in machine elements having ferrous metal frictional bearing surfaces which after assembly of the elements and said surfaces in closely fitting and lubricated operative relationship tend to become scuffed and scored during the initial stage of operation, the improvement which comprises, prior to the assembly and operation of said elements pretreating one of said ferrous surfaces with maleic acid under suitable conditions to cause chemical interaction therebetween, and for a period of time sufficient to preform on said surface an integral thin tenacious film adapted to facilitate and prevent scuffing and scoring during the breaking-in operation.

5. An improved machine element having a ferrous frictional bearing surface, in final condition for assembly and operation, shaped to provide closely fitting and lubricated contact with an other element under initial breaking-in conditions tending to cause scufiing and scoring of said surface, said surface being provided with a preformed integral thin tenacious film constituted by a chemical reaction product of said surface and maleic acid, and adapted to facilitate breakmg-in and to prevent scufling and scoring of said surface after assembly and operation of said elements.

6. An improved machine element having a ferrous frictional bearing surface, in final condition for assembly and operation, shaped to provide closely fitting and lubricated contact with another element under initial breaking-in conditions tending to cause scufiing and scoring of said surface, said surface being provided with a preformed integral thin tenacious film constituted by a chemical reaction product of said surface and a watersoluble carboxylic acid having a hydroxy substituent, and adapted to facilitate breaking-in and to prevent scuffing and scoring of said surface after assembly and operation of said elements.

7. An improved machine element having a ferrous frictional bearing surface, in final condition for assembly and operation, shaped to provide closely fitting and lubricated contact with another element under initial breaking-in conditions tending to cause scumng and scoring of said surface, said surface being provided with a preformed integral thin tenacious film constituted 8 by a chemical reaction product of said surface and a water-soluble polycarboxylic acid having a by.- droxy substituent, and adapted to facilitate breaking-in and to prevent scufling and scoring of said surface after assembly and operation of said elements.

8. An improved machine element having a ferrous frictional bearing surface, in final condition for assembly and operation, shaped to provide closely fitting and lubricated contact with another element under initial breaking-in conditions tending to cause scufiing and scoring of said surface, said surface being provided with a preformed integral thin tenacious film constituted by a chemical reaction product of said surface and a water-soluble polycarboxylic acid adapted to facilitate breaking-in and to prevent scufling and scoring of said surface after assembly and operation of said elements.

9. An improved machine element having a ferrous frictional bearing surface, in final condition for assembly and operation, shaped to provide closely fitting and lubricated contact with another element under initial breaking-in conditions tending to cause scufilng and scoring of said surface, said surfac being provided with a preformed integral thin tenacious film constituted by a chemical reaction product of said surface and a water-soluble carboxylic acid having unsaturated carbon atoms adjacent a carboxyl group, and adapted to facilitate breaking-in and to preventscufiing and scoring of said surface after assembly and operation of said elements.

BRUCE B. FARRINGTON. ROBERT L. HUMIPHREYS. RONALD T. MACDONALD. 

